I would recommend that you have them printed on sticker sheets and stick it on Hi Art cardboard.
Most digital places wont be able to print on cardboard thicker than 12pt which is still thin to build a HQ.
For good service and nice prices I would recommend Urgence Copies on ontario street . Its five minutes from the Frontenac metro station.
You can even send them, your files and pick up your stuff the next day so you wont have to go twice.
urgencecopies.com
if you want more info.